Advanced experiments for characterizing and understanding hydrogen-assisted mechanical degradation

金属中氢的存在往往导致断裂模式从延性的穿晶向不那么延性或脆性的沿晶转变。为了理解氢诱导降解的作用和机制，有必要了解晶粒内部的局部氢浓度，特别是在材料的晶界等不均匀性处。在本项目中，基于afm的扫描开尔文探针力显微镜（SKPFM）将用于研究粗晶和脉冲电沉积纳米晶镍样品中的局部氢分布。这些样品将在一个新设计的电化学电池中充满氢。将细胞整合到AFM中，使我们能够研究i) GBs类型（例如倾斜或扭曲），ii) GBs的分离，iii) GBs的位错堆积和iv)晶粒尺寸对局部氢含量和氢扩散速率的影响。为了评估氢含量与局部力学性能之间的关系，将进行原位纳米压痕测量。研究施加的外单轴拉伸应力对确定的GB塑性的贡献将是本工作的另一个主题。此外，还将评估GBs处的偏析对加工硬化和变形过程的影响以及对局部氢浓度的影响。

Presence of hydrogen in metals causes often a change in fracture mode from ductile transgranular to less ductile or brittle intergranular. For understanding the role and mechanisms of hydrogen induced degradation, it is necessary to know the local hydrogen concentration inside the grains and more especially at material inhomogeneities like grain boundaries (GBs). During this project, AFM-based scanning Kelvin probe force microscopy (SKPFM) will be used for studying local hydrogen distribution at coarse grained and pulse electrodeposited nanocrystalline nickel samples. The samples will be charged with hydrogen in a newly designed electrochemical cell. The incorporation of the cell into an AFM, enables us to study the impacts of i) type of GBs (e.g. tilt or twist), ii) segregations at the GBs, iii) pile-up of dislocations at the GBs and iv) grain sizes, on the local hydrogen content and hydrogen diffusion rate. In-situ nanoindentation measurements will be performed in order to evaluate the relationship between hydrogen content with local mechanical properties. Studying the contributions of applied external uniaxial tensile stress on the plasticity of a defined GB will be another subject of this work. Moreover, the influence of segregations at the GBs on work hardening and deformation processes in addition to their impact on the local hydrogen concentration will be evaluated.